How much memory do you need to run in 64bit mode is 6gb enough?

You can run in 64 bit mode with only 2gig of ram but it depends on what you want Io do.

I have 32GIG. I would reckon that 8 would be that absolute bare minimum just to run Windows x64 let alone a DAW with samples etc.

I run Windows 7 64 bit and SONAR 32 bit (mainly, although use 64 bit sometimes) with a "mere" 4GB.  Absolutely fine.

It does depend on what you will be doing. If you are loading a lot of samples, 6 GB will be on the low side. If you are mainly editing audio or using soft synths, it may be OK. My previous DAW had 8 GB and it was not enough for what I needed to do.

Windows takes up most of 4gb. If you do anything worthwhile you will be swapping to disk like the old days. Minimum of 6gb. 8gb is even better. I like 16 and with what I do, I never get below 6gb free.

16gb is what you should be looking for as a minimum. If you have anything below 8Gb it's almost certainly a bottleneck.

6 GB is probably enough for most people.

Windows takes up about 700MB - no idea what yours is filling the other 3GB with!

There's a heck of a lot more than just "Windows" going on, that's only a generic term.
Charly is right here, environmentally around 3Gb is generally taken up straight away before you do anything. Then memory starts swapping to hard drive if you don't have enough of it.
 
Well anyway ... you can find out yourself...
https://technet.microsoft.com/en-gb/sysinternals/bb896653.aspx
 
In my view pretty much every PC (whatever the requirement) should really have 8Gb minimum installed nowadays. Double it for DAW's.

the op should see how it goes with 6, and add more if necessary